This invention relates to novel catalysts, catalyst systems, methods of production of olefin polymers, and elastomeric olefin polymers, particularly crystalline and amorphous block polymers by use of the novel catalysts of the invention. A principal area of interest is the preparation and use of novel cyclopentadienyl or indenyl metallocene catalysts to produce elastomeric stereoblock polymers, and methods of control of catalyzed polymeric reactions to produce polymers having properties ranging from crystalline thermoplastics to thermoplastic elastomers to amorphous gum elastomers.
Crystalline, amorphous, and elastic polypropylenes are known. Crystalline polypropylenes are generally regarded as comprising of predominantly isotactic or syndiotactic structures and amorphous polypropylene is regarded as comprising predominantly of an atactic structure. U.S. Pat. Nos. 3,112,300 and 3,112,301 both of Natta, et. al. describe isotactic and prevailingly isotactic polypropylene.
U.S. Pat. No. 3,175,199 to Natta et al. describes an elastomeric polypropylene which can be fractioned out of a polymer mixture containing prevailingly isotactic and atactic polypropylenes. When separated from the polymer mixture, a fraction of this polymer showed elastomeric properties which were attributed to a stereoblock structure comprising alternating blocks of isotactic and atactic stereosequences.
Previously, the catalysts used to produce stereoblock amorphous crystalline polypropylenes consisted of heterogeneous catalysts comprising titanium or vanadium halides on a support (Natta and Crespi 1965; German Patent DD 300,293 of Arnold et al.), or tetralkyl zirconium or titanium on a metal oxide support U.S. Pat. No. 4,335,225 of Collette (du Pont). These heterogeneous catalysts do not consist of single sites, but of multiple sites and thus produce a mixture of polymeric materials which can be fractionated by extraction into suitable solvents. The various fractions typically have different molecular weights and molecular weight distributions and vary in their physical properties.
Metallocene catalysts are capable of polymerizing alpha olefins to atactic, isotactic, or syndiotactic structures. In particular, rigid bridged indenyl metallocenes represented by the general structure A and B are known in the art where M=Ti, Zr, and Hf: 
As disclosed by Ewen (xe2x80x9cMechanisms of Stereochemical Control in Propylene Polymerizations with Soluble Group 4B Metallocene/Methylalumoxane Catalystsxe2x80x9d J. Am. Chem. Soc. 1984, 106, 6355-6364), stereorigid catalysts of racemic geometry A produce isotactic polypropylene whereas stereorigid catalysts of meso geometry B produce atactic polypropylene.
A metallocene catalyst was disclosed which yields elastomeric polypropylene (Chien, Llinas et al. 1991; Cheng, Babu et al. 1992; Llinas, Dong et al. 1992). This catalyst had rather low activity (3.5xc3x97105 gm polymer/mol Ti.hr) and yielded polypropylenes with molecular weights less than Mw=200,000. This polymer was more homogeneous in its composition, and was completely soluble in diethyl ether. Polypropylenes produced with this catalyst had melting points below 70xc2x0 C., with elongations up to 1300% and tensile strength of 1750 psi.
Accordingly, there is a need for more active catalyst systems, the structure of which can be controlled in the reaction system during polymerization to produce a selected ratio of atactic/isotactic stereosequences, resulting in high molecular weight polymers with narrow molecular weight distributions having preselected properties, including thermoplastic elastomeric properties.
It is an object and advantage of this invention to provide a new class of metallocene catalysts, and methods of polymerization employing the catalysts to produce a wide range of alpha olefin polymers, including isotactic-atactic stereoblock polymers having a broad range of structures, including isotactic stereosequences of varying lengths to provide a preselected range of properties, including highly elastomeric thermoplastic properties.
It is another object and advantage of this invention to provide stereoblock alpha olefin polymers with preselected properties by control of catalyst substituents and process conditions.
It is another object and advantage of this invention to provide processes for preparation of a wide variety of stereoblock polymers through control of the catalyst geometry.
It is another object and advantage of this invention to provide a novel class of polymer systems, including stereoblock polymers having preselected properties.
It is another object and advantage of this invention to provide a novel class of high molecular weight atactic polypropylenes.
Still other objects and advantages of the invention will be evident from the Descriptions, Drawings, and Claims of this application.
This invention is directed to novel metallocene-complex catalysts the structure and activity of which can be controlled to produce a wide range of olefin polymers and co-polymers, and preferably for the production of stereoblock poly alpha-olefins comprising a wide range of preselected amorphous and crystalline segments for precise control of the physical properties thereof, principally elastomeric thermoplastic properties. More specifically, this invention is directed to novel metallocene catalysts and catalyst systems for producing stereoblock polypropylene comprising alternating isotactic and atactic diastereosequences, which result in a wide range of elastomeric properties. The amount and number of crystalline sections, the isotactic pentad content, the number and length of intermediate atactic chains and overall molecular weight are all controllable by the electronic and steric nature of the catalysts and the process conditions. The novel catalysts provided by the present invention are ligand-bearing non-rigid metallocenes the geometry of which can change on a time scale that is slower than the rate of olefin insertion, but faster than the average time to construct (polymerize) a single polymer chain, in order to obtain a stereoblock structure in the produced polyolefins. The symmetry of the catalyst structure is such that upon isomerization the catalyst symmetry alternates between a chiral and an achiral geometry. This geometry alternation can be controlled by selecting ligand type and structure, and through control of polymerization conditions to precisely control the physical properties of the resulting polymers.
This invention includes a novel process for tailoring the block size distribution and resulting properties of the polymer such as the tacticity, molecular weight, molecular weight distribution, melt flow rate, melting point, crystallite aspect ratio, tensile set and tensile strength by varying the structure of the catalyst and the conditions of the polymerization reaction.
In a preferred embodiment the catalysts and methods of this invention produce a novel class of elastomeric polymers comprising units derived from propylene, which have a high molecular weight and a narrow molecular weight distribution, which are homogeneous in their composition. By homogeneous in composition, we mean that if the polymer can be fractionated by whatever solvent or solvent system(s), all the polymer fractions have similar molecular weight distributions Mw/Mn, typically less than 7, preferably less than 5, and most preferred less than 4.
The thermoplastic elastomeric polypropylenes of this invention exhibit elongations to break from 20% to 5000%, typically between 100% and 3000% with tensile sets between 5% and 300%, typically between 10% and 200%, and preferably between 10% and 70%. Tensile strengths for these polypropylenes range from 100 psi to 6000 psi, typically between 400 psi and 5000 psi. The crystallinity of the polymers range from amorphous materials with no melt, to crystalline thermoplastic with melting points of about 165xc2x0 C. Preferably he melting points range from about 500 to about 165xc2x0 C.
The catalyst system of the present invention consists of the transition metal component metallocene in the presence of an appropriate cocatalyst. In broad aspect, the transition metal compounds have the formula: 
in which M is a Group 3, 4 or 5 Transition metal, a Lanthanide or an Actinide, X and Xxe2x80x2 are the same or different hydride, halogen, hydrocarbyl, or halohydrocarbyl substituents, and L and Lxe2x80x2 are the same or different substituted cyclopentadienyl or indenyl ligands, in combination with an appropriate cocatalyst. Exemplary preferred transition metals include Titanium, Hafnium, Vanadium, and the present best mode, Zirconium. An exemplary Group 3 metal is Yttrium, a Lanthanide is Samarium, and an Actinide is Thorium.
The transition metal substituents X and Xxe2x80x2 may be the same or different hydride, halogen, hydrocarbyl, or halohydrocarbyl substituents, X and Xxe2x80x2 are preferably halogen, alkoxide, or C1 to C7 hydrocarbyl.
The ligands L and Lxe2x80x2 may be any mononuclear or polynuclear hydrocarbyl or silahydrocarbyl, typically a substituted cyclopentadienyl ring. Preferably L and Lxe2x80x2 have the formula: 
where R1, R2, and R3 may be the same or different alkyl, alkylsilyl, or aryl substituents of 1 to about 30 carbon atoms. Most preferably, R1 is an aryl group, such as a substituted phenyl, biphenyl, or naphthyl group, and R2 and R3 are connected as part of a ring of 3 or more carbon atoms.
Especially preferred for L or Lxe2x80x2 of Formula 1 is a 2-arylindene of formula: 
Where R4, R5, R6, R7 and R8 may be the same or different hydrogen, halogen, aryl, hydrocarbyl, silahydrocarbyl, or halohydrocarbyl substituents. That is, R1 of Formula 2 is R4-R8-substituted benzene, and R2, R3 are cyclized in a 6-C ring to form the indene moiety. Particularly preferred 2-aryl indenes include as present best mode compounds: 2-phenylindene, 2-(3,5-dimethylphenyl)indene; 2-(3,5-bis-trifluoromethylphenyl)indene; 2-(4, -fluorophenyl)indene; 2-(2,3,4,5-tetrafluorophenyl)indene; 2-(2,3,4,5,6-pentafluorophenyl)indene; 2-(1-naphthyl)indene; 2-(2-naphthyl)indene; 2-[(4-phenyl)phenyl]indene; and 2-[(3-phenyl)phenyl]indene.
Preferred metallocenes according to the present invention include: bis[2-phenylindenyl]zirconium dichloride; bis[2-phenylindenyl]zirconium dimethyl; bis[2-(3,5-dimethylphenyl)indenyl]zirconium dichloride; bis[2-(3,5-bis-trifluoromethylphenyl)indenyl]zirconium dichloride; bis[2-(4 ,-fluorophenyl)indenyl]zirconium dichloride; bis[2-(2,3,4,5,-tetrafluorophenyl)indenyl]zirconium dichloride; bis[2-(2,3,4,5,6-pentafluorophenyl)indenyl]zirconium dichloride; bis[2-(1-naphthyl)indenyl]zirconium dichloride; bis[2-(2-naphthyl)indenyl]zirconium dichloride; bis[2-[(4-phenyl)phenyl]indenyl]zirconium dichloride; bis[2-[(3-phenyl)phenyl]indenyl]zirconium dichloride; and the same hafnium compounds such as: bis[2-phenyl(indenyl)hafnium dichloride; bis[2-phenyl(indenyl)]hafnium dimethyl; bis[2-(3,5-dimethylphenyl)indenyl]hafnium dichloride; bis[2-(3,5-bis-trifluoromethyphenyl)indenyl]hafnium dichloride; bis[2,(4-fluorophenyl)indenyl]hafnium dichloride; bis[2-(2,3,4,5-tetrafluorophenyl)indenyl]-hafnium dichloride; bis[2-(2,3,4,5,6-pentafluorophenyl)indenyl]hafnium dichloride; bis[2-(1-naphthyl)indenyl]hafnium dichloride; bis[2-(2-naphthyl))indenyl]hafnium dichloride; bis[2-[(4-phenyl)phenyl)indenyl]hafnium dichloride; bis[2-[(3-phenyl)phenyl]indenyl]hafnium dichloride; and the like.
FIG. 1 shows the structure of a preferred catalyst bis-(2-phenylindenyl)zirconium dichloride. As shown in the figure, this complex crystallizes in two conformations, a racemic-like conformation 1a and a meso-like conformation 1b.
The Examples disclose a method for preparing the metallocenes in high yield. Generally, the preparation of the metallocenes consists of forming the cyclopentadienyl or indenyl ligand followed by metallation with the metal tetrahalide to form the complex.
Appropriate cocatalysts include alkylaluminum compounds, methylaluminoxane, or modified methylaluminoxanes of the type described in the following references: U.S. Pat. No. 4,542,199 to Kaminsky, et al,; Ewen, J. Am. Chem. Soc., 106 (1984), p. 6355; Ewen, et al., J. Am. Chem. Soc. 109 (1987) p. 6544; Ewen, et al., J. Am. Chem. Soc. 110 (1988), p. 6255; Kaminsky, et al, Angew. Chem., Int. Ed. Eng. 24 (1985), p. 507. Other cocatalysts which may be used include Lewis or protic acids, such as B(C6F5)3 or [PhNMe2H]+B(C6F5)4xe2x88x92, which generate cationic metallocenes with compatible non-coordinating anions in the presence or absence of alkylaluminum compounds. Catalyst systems employing a cationic Group 4 metallocene and compatible non-coordinating anions are described in European Patent Applications 277,003 and 277,004 filed on Jan. 27, 1988 by Turner, et al.; European Patent Application 427,697-A2 filed on Oct. 9, 1990 by Ewen, et al.; Marks, et al., J. Am. Chem. Soc., 113 (1991), p. 3623; Chien, et al., J. Am. Chem. Soc., 113 (1991), p. 8570; Bochmann et al., Angew. Chem. Intl. Ed. Engl. 7 (1990), p. 780; and Teuben et al., Organometallics, 11 (1992), p. 362, and references therein.
The catalysts of the present invention consist of non-rigid metallocenes which can change their geometry on a time scale that is between that of a single monomer insertion and the average time of growth of a polymer chain. This is provided by a non-rigid metallocene catalyst comprising of cyclopentadienyl ligands substituted in such a way that they can alternate in structure between racemic-like and meso-like geometries. This is achieved in the present invention by utilizing unbridged cyclopentadienyl ligands with a 1,2,4-substitution pattern on the cyclopentadienyl moiety. This substitution pattern insures that the ligand is achiral and will not result in diastereomers upon complexation with the metal, thus avoiding unwieldy separation of isomeric metallocenes. In addition, this substitution pattern provides catalysts which can isomerize between a meso-like and racemic-like geometry.
In one of many embodiments, these catalyst systems can be placed on a suitable support such as silica, alumina, or other metal oxides, MgCl2, or other supports. These catalysts can be used in the solution phase, in slurry phase, in the gas phase, or in bulk monomer. Both batch and continuous polymerizations can be carried out. Appropriate solvents for solution polymerization include aliphatic or aromatic solvents such as toluene, benzene, hexane, heptane, as well as halogenated aliphatic or aromatic solvents such as CH2Cl2, chlorobenzene, flourobenzene, hexaflourobenzene or other suitable solvents. Various agents can be added to control the molecular weight, including hydrogen, silanes and metal alkyls such as diethylzinc.
The metallocenes of the present invention, in the presence of appropriate cocatalysts, are useful for the polymerization of ethylene and alpha-olefins, such as propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and combinations thereof. The polymerization of olefins is carried out by contacting the olefin with the catalyst systems comprising the transition metal component and in the presence of an appropriate cocatalyst, such as an alumoxane, or a Lewis acid such as B(C6F5)3. The catalysts are more active than the Chien catalysts for the polymerization of ethylene and alpha olefins with productivities of 3xc3x97106 g polymer/mol Zr.hr for ethylene being readily obtained.
The metallocene catalyst systems of the present invention are particularly useful for the polymerization of propylene to produce polypropylenes with novel elastomeric properties. By elastomeric, we mean a material which tends to regain its shape upon extension, or one which exhibits a positive power of recovery at 100%, 200% and 300% elongation. The properties of elastomers are characterized by several variables. The initial modulus (Mi) is the resistance to elongation at the onset of stretching. This quantity is simply the slope at the beginning of the stress-strain curve. Upon overstretching, the polymer sample eventually ruptures. The rupture point yields two important measurements, the tensile strength (Tb) and the ultimate elongation (Eb). These values are the stress and percent elongation at the break, respectively. The tensile set (TS) is the elongation remaining in a polymer sample after it is stretched to 300% elongation and allowed to recover. An additional measure of the reversibility of stretching is the percent recovery (PR), which is given by the equation: 100(Lmaxxe2x88x92Lrelax)/(Lmaxxe2x88x92Linit).
It is believed that the elastomeric properties of the polypropylenes of this invention are due to an alternating block structure comprising of isotactic and atactic stereosequences. Without being bound by theory, it is believed that isotactic block stereosequences provide crystalline blocks which can act as physical crosslinks in the polymer network.
The structure of the polymer can be described in terms of the isotactic pentad content [mmmm] which is the percentage of isotactic stereosequences of 5 contiguous stereocenters, as determined by 13C NMR spectroscopy (Zambelli, Locatello et al. 1975). The isotactic pentad content of statistically atactic polypropylene is approximately 6.25%, while that of highly isotactic polypropylene can approach 100%.
While it is possible to produce polypropylenes with a range of isotactic pentad contents, the elastomeric properties of the polymer will depend on the distribution of isotactic (crystalline) and atactic (amorphous) stereosequences. Thermoplastic elastomers consist of amorphous-crystalline block polymers, and thus the blockiness of the polymer determines whether it will be elastomeric.
The blockiness of the polymer can be described in terms of the fraction of isotactic stereosequences of four or more stereocenters (Randall 1976) which we will denote as the isotactic Block Index,  less than BI greater than . The isotactic Block Index can be determined directly from the pentad distribution and is given by (Randall 1976) as:
 less than BI greater than =4+2[mmmm]/[mmmr].
The isotactic Block Index for purely atactic polypropylene is  less than BI greater than =5, while that for highly isotactic polypropylene can exceed  less than BI greater than =104 (Collette, Ovenall et al 1989).
We have discovered that the structure, and therefore the properties of the polypropylenes obtained with the catalysts of the present invention are dependent on the olefin concentration, the temperature of the polymerization, the nature of the transition metal, the ligands on the metallocene, and the nature of the cocatalyst. Under certain circumstances (solution polymerization at low propylene pressures) we have observed that the isotactic pentad content [mmmm] and the Block Index,  less than BI greater than , of the resulting polypropylene increase with decreasing polymerization temperature. Under other conditions (polymerization in bulk monomer) we see the isotactic pentad content increase with increasing temperature.
The structure, and therefore the properties of the obtained polypropylenes also depends on the propylene pressure during the polymerization reaction. The isotactic pentad content [mmmm] and the isotactic Block Index,  less than BI greater than , of the polypropylenes increase with increasing propylene pressure. The productivity and average molecular weight of the polypropylenes also increase with increasing propylene pressure.
The structure, and therefore the properties of the obtained polypropylenes also depend on the nature of the ligands bound to the transition metal. For example, for catalysts derived from bis[2-(3,5-bis-trifluoromethylphenyl)indenyl]zirconiumdichloride metallocene, isotactic pentad contents up to [mmmm]=71% and isotactic Block Indexes  less than BI greater than =15.3 can be readily obtained, with even higher values indicated.
It will be appreciated from the illustration examples that this catalyst system provides an extraordinary broad range of polymer properties from the polymerization process of this invention. Isotactic pentad contents from [mmmm]=6.1% to [mmmm]=71% can be readily obtained by suitable manipulation of the metallocene catalyst, the reaction conditions, or the cocatalyst to give polymers which range in properties from gum elastomers to thermoplastic elastomers to flexible thermoplastics, and indeed, to relatively rigid thermoplastics.
This invention also provides a novel process for tailoring the block size distribution as reflected in the isotactic pentad content [mmmm] and properties of the polymer such as melting point, tensile set and tensile strength by varying the structure of the catalyst and the conditions of the polymerization reaction. The invention provides a process whereby the isotactic pentad content and the properties of the polymer can be tailored through changes in the pressure of monomer, the temperature of polymerization, the nature of the transition metal, the nature of the ligands and the nature of the cocatalyst.
Without being bound by theory, it is believed that it is critical for the present invention to have a catalyst which can isomerize on a time scale that is slower than the rate of olefin insertion but faster than the average time to construct a single polymer chain in order to obtain a block structure. In addition, to produce elastomeric polymers, the catalyst complex isomerizes between a chiral racemic-like and an achiral meso-like geometry. This is provided in the present invention by metallocene catalysts comprising of unbridged cyclopentadienyl-based ligands which are substituted in such a way that they can exist in racemic or meso-like geometries.
Based on the evidence to date, it appears that the rotation of the cyclopentadienyl ligands provides a mechanism for the alternation of catalyst geometry. The average block size distribution for a polymer produced with a catalyst which can change its state is controlled by the relative rate of polymerization versus catalyst isomerization as well as the steady-state equilibrium constant for the various coordination geometries (e.g. chiral vs. achiral). The catalysts of this invention provide a means of producing polypropylenes and other alpha olefins with a wide range of isotactic and atactic block lengths by changing the substituents on the cyclopentadienyl ligands of the metallocene. It is believed that modification of the cyclopentadienyl ligands and/or the nature of the transition metal will alter one or more of the following: The rate of polymerization, the rate of catalyst isomerization, and the steady-state equilibrium constant between the various coordination geometries, all of which will affect the block lengths and block length distribution in the resulting polymer. For example, it is believed that introduction of larger substituents on the cyclopentadienyl ligands will slow the rate of rotation and thereby increase the block lengths in the polymer. 
The increase in isotactic pentad content [mmmm] and Block Index  less than BI greater than  with propylene pressure appears due to an increase in the relative rate of polymerization relative to catalyst isomerization. It is further believed that the increase of isotactic pentad content [mmmm] and Block Index  less than BI greater than  as the temperature of polymerization is decreased for polymerizations carried out in solution is also a result of increasing the relative rate of polymerization relative to isomerization with decreasing temperature. Thus, the present invention provides a rational method of control of the length of isotactic blocks, and therefore the melting points, tensile strengths, and tensile modulus, with changes in the process conditions.
The importance of freely rotating ligands is demonstrated by the polymerization of propylene with the bridged racemic and meso isomers of ethylene-1,2-bis-(2-phenyl-1-indenyl)zirconium dichloride, (Catalyst K, L). Polymerization of propylene with the rac isomer, Catalyst K, yielded isotactic polypropylene. Polymerization of propylene with the rac/meso mixture yielded a blend of atactic and isotactic polypropylene rather than a block copolymer. That this mixture was a blend was demonstrated by fractionation of the atactic material with pentane. The pentane-soluble fraction was amorphous, atactic polypropylene, and the pentane-insoluble fraction was crystalline, isotactic polypropylene.
The invention also includes novel bridged catalysts of the structure: 
Wherein L, Lxe2x80x2, M, X, and Xxe2x80x2 are as above, and B is a structural bridge between the ligands L, Lxe2x80x2 imparting stereorigidity to the catalyst in either/both rac and meso geometries, B being preferably selected from a C1-C4 alkylene radical, and Ge, Si, P and In hydrocarbyl radicals.
The polymers of the present invention in one embodiment are a novel class of thermoplastic elastomers made up of propylene homopolymers of molecular weights ranging from 20,000 to above about 2 million. The average molecular weights of the polypropylenes are typically high, as molecular weights on the average of 1,600,000 are readily obtainable and even higher are indicated. The processability of polymers in fiber and film applications is a function of the molecular weight or melt flow rate of the material. It is well known that polymers with high molecular weights (low melt flow rates), while advantageous in certain applications, are quite difficult to process and typically require post treatment with peroxide to increase the melt flow rate. This involves an extra processing step and can add significantly to the cost of the product. Accordingly, hydrogen is used in many polymerization processes to control molecular weight during the reaction (Welborn U.S. Pat. No. 5,324,800 and refs therein). Homogeneous metallocene catalysts are known to be quite sensitive to hydrogen (Kaminsky Makromol. Chem., Rapid Commun. 1984, 5, 225). We have found that the molecular weight and melt flow rate of the polymers of this invention can easily be controlled by using small amounts of hydrogen. For example, for the polymers of this invention, while a melt flow rate of  less than 0.1 dg/min (high molecular weight, low processability) is readily obtained in the absence of hydrogen, the addition of as little as 0.17 mmol H2/mol propylene can result in an increase in melt flow rate to 25 dg/min (lower molecular weight, high processability). The melt flow rate is the amount of polymer that extrudes under a 2.0 Kg standard weight through a standard orifice at a standard temperature. In contrast, the MFR of the Collette (du Pont) polypropylene polymers is  less than 0.1 dg/min, even after 11 mmol H2/mol polypropylene, a clear difference in kind.
The molecular weight distribution (Mw/Mn) of polymers made with heterogeneous catalysts is known to be quite broad, especially compared with similar polymers made with homogeneous metallocene based catalysts. Davey, et al (U.S. Pat. No. 5,322,728) have described the difficulties of processing polymers having broad molecular weight distributions, especially in the manufacture of fiber products. In contrast, the molecular weight distributions of the polymers of the present invention are quite low, with typical polydispersities, Mw/Mn, ranging from 1.7 to 5. However, by control of reaction conditions, higher molecular weight distributions also can be obtained, e.g., polydispersities of 5-20 are easily produced.
The polypropylenes of the present invention have isotactic pentad contents ranging from [mmmm]=6.3%, corresponding to statistically atactic polypropylenes, to [mmmm]=71%, corresponding to an elastomeric polypropylene with high isotacticity. The polypropylenes of the present invention range from amorphous atactic polypropylenes with no melting point, to elastomeric polypropylenes of high crystallinity with melting points up to 165xc2x0 C.
Accordingly, because of the wide range of structures and crystallinities, the polypropylenes of the present invention exhibit a range of properties from gum elastomers, to thermoplastic elastomers, to flexible thermoplastics. The range of elastomeric properties for the polypropylenes is quite broad. Elongations to break typically range from 100% to 3000%, tensile strengths range from 400 psi to over 5000 psi. Tensile set at 300% elongation as low as 32% and below can be readily obtained, and tensile set is generally below about 70%. Cold drawing results in improved elastic recoveries, a valuable property for films and fibers.
The polypropylenes of the present invention exhibit low creep, particularly for samples of higher crystallinity. They can be melt spun into fibers, or can be cast into transparent, tough, self-supporting films with good elastic recoveries. Thin films of elastomeric polypropylenes with isotactic pentad contents [mmmm]=30% are slightly opaque, but exhibit stress-induced crystallization. Upon isolation of an elastomeric polypropylene of this invention from solution under vacuum, the polymer was observed to make a closed-cell foam, with a spongy texture. The elastomeric polypropylenes can also be cast into molded articles. Samples of lower crystallinity were observed to adhere quite well to glass.
The elastomeric polymers of the present invention form excellent adhesives. They adhere well to glass, paper, metals and other materials. A sample of lower crystallinity was observed to adhere well to paper, allowing a manila folder to be attached to and supported on a metal filing cabinet. Upon removal of the material, the sample remained adhered to the paper and no residue was left on the metal surface.
The polypropylenes of the present invention can be blended with isotactic polypropylenes. The melting points and heats of fusion of the blends increase steadily with increasing mole fraction of isotactic polypropylene in the blend.
The utility of the polymers of the present invention are evident and quite broad, including without limitation: films; fibers; foams; molded articles; adhesives; and resilient and elastomeric objects. As they are completely compatible with isotactic polypropylenes, they are ideal candidates as additives for blends to improve the toughness and impact strength of isotactic polypropylenes.